A ladder is a vertical or inclined set of rungs or steps. There are two types of ladders: rigid ladders that can be leaned against a vertical surface such as a wall, and rope ladders that are hung. The vertical members of a rigid ladder are called stringers, rails or stiles. Rigid ladders are usually portable, but some types are permanently affixed to buildings. They are commonly made of metal, wood, or fiberglass, and tough plastic.